I create simple user control for example just to take input textbox, and created data type using umbraco usercontrol wrapper.  

http://www.nibble.be/?p=24

  if (Page.IsPostBack)
            {
                             if (TextBox1.Text.Length > 0)
                              {
                                   umbracoValue = TextBox1.Text;
                               }
                else
                         {
                                if (text.Length > 0)
                                         {
                                                  umbracoValue = "1234";
                           }                   
                }

                }      

label1.text= umbracoValue;     

        public object value
        {
            get
            {
                return umbracoValue;
            }

            set
            {
                umbracoValue = value.ToString();
            }
        }

Problem: using that data type i can create simple text input. when i press "save and publish" it works fine and i can get value next time.

but when i create content and "Save", when i close the browser or open content next time value is empty or lost. i checked App-data/umbraco.config file its empty value.

my questions is .

when i use user control as datatype where umbraco save that value in database? and how to retrive that value from database? using c#.

thanks in advance.